at the end of the day it's the same game, so why the huge difference?
thats were your thinking is flawed, its a differrent game with some similar rules.
100 meter dash and marathon are both running, but you can't compare them.

Your goals are different, in a cash game you want to maximize your winning for each specific hand, as you are free to leave whenever yu want.
In a tournament your goal is to come ITM, the results of any specific hands is just the means to the goal